/*-------------------------------------------------------------------------
 *
 * nodeNamedtuplestorescan.c
 *      routines to handle NamedTuplestoreScan nodes.
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *      src/backend/executor/nodeNamedtuplestorescan.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "executor/execdebug.h"
#include "executor/nodeNamedtuplestorescan.h"
#include "miscadmin.h"
#include "utils/queryenvironment.h"

static TupleTableSlot *NamedTuplestoreScanNext(NamedTuplestoreScanState *node);

/* ----------------------------------------------------------------
 *        NamedTuplestoreScanNext
 *
 *        This is a workhorse for ExecNamedTuplestoreScan
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
NamedTuplestoreScanNext(NamedTuplestoreScanState *node)
{
    TupleTableSlot *slot;

    /* We intentionally do not support backward scan. */
    Assert(ScanDirectionIsForward(node->ss.ps.state->es_direction));

    /*
     * Get the next tuple from tuplestore. Return NULL if no more tuples.
     */
    slot = node->ss.ss_ScanTupleSlot;
    (void) tuplestore_gettupleslot(node->relation, true, false, slot);
    return slot;
}

/*
 * NamedTuplestoreScanRecheck -- access method routine to recheck a tuple in
 * EvalPlanQual
 */
static bool
NamedTuplestoreScanRecheck(NamedTuplestoreScanState *node, TupleTableSlot *slot)
{
    /* nothing to check */
    return true;
}

/* ----------------------------------------------------------------
 *        ExecNamedTuplestoreScan(node)
 *
 *        Scans the CTE sequentially and returns the next qualifying tuple.
 *        We call the ExecScan() routine and pass it the appropriate
 *        access method functions.
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecNamedTuplestoreScan(PlanState *pstate)
{
    NamedTuplestoreScanState *node = castNode(NamedTuplestoreScanState, pstate);

    return ExecScan(&node->ss,
                    (ExecScanAccessMtd) NamedTuplestoreScanNext,
                    (ExecScanRecheckMtd) NamedTuplestoreScanRecheck);
}


/* ----------------------------------------------------------------
 *        ExecInitNamedTuplestoreScan
 * ----------------------------------------------------------------
 */
NamedTuplestoreScanState *
ExecInitNamedTuplestoreScan(NamedTuplestoreScan *node, EState *estate, int eflags)
{
    NamedTuplestoreScanState *scanstate;
    EphemeralNamedRelation enr;

    /* check for unsupported flags */
    Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));

    /*
     * NamedTuplestoreScan should not have any children.
     */
    Assert(outerPlan(node) == NULL);
    Assert(innerPlan(node) == NULL);

    /*
     * create new NamedTuplestoreScanState for node
     */
    scanstate = makeNode(NamedTuplestoreScanState);
    scanstate->ss.ps.plan = (Plan *) node;
    scanstate->ss.ps.state = estate;
    scanstate->ss.ps.ExecProcNode = ExecNamedTuplestoreScan;

    enr = get_ENR(estate->es_queryEnv, node->enrname);
    if (!enr)
        elog(ERROR, "executor could not find named tuplestore \"%s\"",
             node->enrname);

    Assert(enr->reldata);
    scanstate->relation = (Tuplestorestate *) enr->reldata;
    scanstate->tupdesc = ENRMetadataGetTupDesc(&(enr->md));
    scanstate->readptr =
        tuplestore_alloc_read_pointer(scanstate->relation, EXEC_FLAG_REWIND);

    /*
     * The new read pointer copies its position from read pointer 0, which
     * could be anywhere, so explicitly rewind it.
     */
    tuplestore_rescan(scanstate->relation);

    /*
     * XXX: Should we add a function to free that read pointer when done?
     *
     * This was attempted, but it did not improve performance or memory usage
     * in any tested cases.
     */

    /*
     * Miscellaneous initialization
     *
     * create expression context for node
     */
    ExecAssignExprContext(estate, &scanstate->ss.ps);

    /*
     * initialize child expressions
     */
    scanstate->ss.ps.qual =
        ExecInitQual(node->scan.plan.qual, (PlanState *) scanstate);

    /*
     * tuple table initialization
     */
    ExecInitResultTupleSlot(estate, &scanstate->ss.ps);
    ExecInitScanTupleSlot(estate, &scanstate->ss);

    /*
     * The scan tuple type is specified for the tuplestore.
     */
    ExecAssignScanType(&scanstate->ss, scanstate->tupdesc);

    /*
     * Initialize result tuple type and projection info.
     */
    ExecAssignResultTypeFromTL(&scanstate->ss.ps);
    ExecAssignScanProjectionInfo(&scanstate->ss);

    return scanstate;
}

/* ----------------------------------------------------------------
 *        ExecEndNamedTuplestoreScan
 *
 *        frees any storage allocated through C routines.
 * ----------------------------------------------------------------
 */
void
ExecEndNamedTuplestoreScan(NamedTuplestoreScanState *node)
{
    /*
     * Free exprcontext
     */
    ExecFreeExprContext(&node->ss.ps);

    /*
     * clean out the tuple table
     */
    ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);
    ExecClearTuple(node->ss.ss_ScanTupleSlot);
}

/* ----------------------------------------------------------------
 *        ExecReScanNamedTuplestoreScan
 *
 *        Rescans the relation.
 * ----------------------------------------------------------------
 */
void
ExecReScanNamedTuplestoreScan(NamedTuplestoreScanState *node)
{
    Tuplestorestate *tuplestorestate = node->relation;

    ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);

    ExecScanReScan(&node->ss);

    /*
     * Rewind my own pointer.
     */
    tuplestore_select_read_pointer(tuplestorestate, node->readptr);
    tuplestore_rescan(tuplestorestate);
}
